This invention relates to a flying spot scanning system for communicating video information to a scanned medium, and more particularly to a scanning system which utilizes a multifaceted rotating polygon for controlling the scanning cycles.
Much attention has been given to various optical approaches in flying spot scanning for the purpose of imparting the information content of a modulated light beam to a scanned medium. Galvanometer arrangements have been used to scan the light across a document for recording its information content thereon. Such arrangements have included planar reflecting mirrors which are driven in an oscillatory fashion. Other approaches have made use of multifaceted mirrors which are driven continuously. Various efforts have been made to define the spot size in order to provide for an optimum utilization of the scanning system.
One such effort is that described in U.S. Pat. No. 3,675,016. The approach used was to make the spot size invariant and as small as possible by defining the dimensions of the focused beam so that only part, preferably half, of a mirror facet is illuminated during scanning. This teaching alludes to generalized techniques for assuring the constancy of the size of the aperture of a rotating mirror scanning system. By either illuminating several facets of the mirror or by directing light in a beam that is sufficiently narrow to assure that less than a full facet is the most that can ever be illuminated by the beam and limiting scanning to that portion of the rotary travel of the facet when such facet is illuminated by all of such light beam. However, such system apertures are dimensionally invariant because the dimensions of the rotating facets have no influence on such apertures.
While the system as described in U.S. Pat. No. 3,675,016 may have advantages over the prior art, nevertheless, various constraints must be imposed upon the spot size and other relationships of optical elements within the system which are not always desirable.
In copending U.S. patent application Ser. No. 309,874, filed on Nov. 27, 1972, now abandoned in favor of Ser. No. 626,167 and assigned to the assignee of the present invention, a flying spot scanning system is provided which does not have constraints imposed upon the spot size and other relationships of optical elements within the system which are not always desirable. As taught therein, a finite conjugate imaging system may be in convolution with the light beam and the rotating polygon. A doublet lens, in series with a convex imaging lens between the light source and the medium provides such arrangement. Additionally, a cylindrical lens is positioned in the optical path between the polygon and the scanned medium to compensate for runout and polygon facet errors.
It is thus an object of the present invention to further improve this flying spot scanning system which may tolerate substantial runout and facet errors.
It is a further object of the present invention to provide a spot scanning system which utilizes a multifaceted rotating polygon for controlling scanning cycles.
It is yet another object of the present invention to provide a spot scanning system which provides an effective uniform spot size at the contact loci of the spot with the scanned medium, with increased system efficiencies.
It is still another object of the present invention to provide a spot scanning system which assures an improved sequence of scanning cycles.
It is also an objective of the present invention to provide a flying spot scanning system which includes as optical elements at least two lenses, characterized by an optical plane having power and the other plane having substantially no power, for increasing the depth of focus of the optical system, as well as compensating for runout and polygon facet errors.
Other objects of the invention will be evident from the description hereinafter presented.